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I've had a good look about and not really found what I was after as far as information on using a Halogen lamp for heating a drum roaster.

I initially was looking at a bend your own electric element as used in a typical oven, (the Quest M3 has this type of element) but always had a question over the thermal lag that there would be and if it would be a potential problem, enter the idea of a Halogen lamp.

It seems there are two common types of lamps, longer and shorter IR wavelength lamps, with typically the shorter wavelength lamps for lighting and the longer wavelengths for heating. Is the difference between the two the temperature that the element runs at causing the longer or shorter IR wavelengths, which has me wonder if a Heating Halogen might be lots longer lived due to the lower running temp???

So, the question is if a typical filament lamp is really only converting something like 15% of the energy input into light and the rest into heat surely ALL lamps are suitable for heating.

I gather that the longer IR wavelengths are better at heating, but why? And if this is the case should I/we be considering proper heating Halogen lamps rather than a proper Lighting Halogen Lamp as the heat source?

Is longevity a concern using a lighting Halogen in a confined space, even though there will be airflow past it as a way to preheat the air before it enters the drum?

There seems to be a better choice of lengths available in the Lighting Halogens for the project I have in mind, up to 600 grams, would also like to be able to get down to 200 grams. Thinking of 2100 Watts at a guess to be able to have some extra juice up my sleeve. The lighting Halogens are also lots cheaper than a true Heating Halogen.

You can go even low with power, if convection and good agitation are used.
I am roasting 500 grams perfectly using 1400W, and 600 grams with some non-uniformity, due to only 10 RPM drum speed. The oven volume is 12 l and is insulated.
The maximum temperature in the oven after 5 minutes with the 1400W halogen on, can reach 280C, with no load.

Thanks for the link Allen, probably looked over that one due to it not being a drum roaster.

So, that gets me to another part of same the question, if this is a drum roaster build, solid drum with perforated back end plate, then the comment about the long and short IR having differing effects on the roast at differing times will probably be negated? as the IR is only heating the drum and the air, thoughts?

Len, the current plan would be to have the lamps underneath the drum with a reflector and some air entry tubes that run parallel to and in between the lamps, this will preheat the incoming air to try to help with varying external environmental changes, and will keep the lamps free of direct contamination.

It would be easy to use both long and short IR lamps as Allan has mentioned in the link. From Allan's second post I gather the longer IR will heat better, but does this translate well to heating the wall of the Drum, or the incoming air?

Having a solid drum may negate the usefulness of halogen heat source, I believe the light will just bounce off the solid metal cylinder. You likely would need to either have a perforated drum or a way to have the lights inside of the drum (not an easy feat for sure). I have seen IR inside of a drum but that was gas IR and I cannot recall which manufacturer used that process.

Len

"If this is coffee, please bring me some tea but if this is tea, please bring me some coffee." ~Abraham Lincoln

Having a solid drum may negate the usefulness of halogen heat source, I believe the light will just bounce off the solid metal cylinder

Short wavelength halogen can function fine as a heat source outside of a solid drum. If we're heating the outer surface of a solid drum then the heat source is of no consequence. Any heat source will do assuming it will provide adequate BTU's and react within a reasonable time.

My previous post was regarding IR heat located inside the drum where the IR will be absorbed by the coffee.

Having a solid drum may negate the usefulness of halogen heat source, I believe the light will just bounce off the solid metal cylinder. You likely would need to either have a perforated drum or a way to have the lights inside of the drum (not an easy feat for sure). I have seen IR inside of a drum but that was gas IR and I cannot recall which manufacturer used that process.

It seems there are two common types of lamps, longer and shorter IR wavelength lamps, with typically the shorter wavelength lamps for lighting and the longer wavelengths for heating. Is the difference between the two the temperature that the element runs at causing the longer or shorter IR wavelengths, which has me wonder if a Heating Halogen might be lots longer lived due to the lower running temp???

Yes, hotter temperature, shorter wavelength.
It is true that longer wavelength IR is more readily absorbed by dark surfaces (including the exterior of a roasting drum) compared to medium or short wavelength. With that in mind, with everything else being equal between two designs, the one with the longer wavelength will allow more of the energy to be absorbed by the drum and less being reflected between various surfaces. As long as the area housing the shorter wavelength lamps is very well insulated, the total energy making it's way to the air and beans will be equal to the one with long wavelength. The only difference would be that the one with longer wavelength would give us a hotter drum temperature and less being absorbed by the nearby metal components of the roaster and somewhat less heating of the air being pulled through this area. I'm not sure if the difference would be enough to be a factor in your decision on which source to choose.
One thing to consider is the problem with varying power levels to halogen lamps. Going below a certain filament temperature will cause a halogen lamp's filament to stop reabsorbing the material that is released into the lamps shell and shorten it's life span. This results in the darkening of the lamps glass and an increase in its temperature. I would go with medium to long wavelength devices that are designed to operate at varying power levels.

Thanks for the extra info and reading, its made me do a few new searches and found a bit of extra info, some of which seems a lil contradictory but all worth while.

I think I've decided to get a typical Lighting Halogen, short IR tube and a proper heating tube long IR tube and might do a proper heating test and log the results, see which one heats a metal plate the quickest or perhaps the most consistently.

Does anyone have any feedback on thermal lag or response times of heating styles vs response times of the Drum, as in a drum will have a certain amount of thermal lag due to mass, will this mean a slow response heat source is fine, or will a quick acting heat source still be worth while?

I like the idea of the Lighting Halogen due to the pricing of them, and the variety of lengths available.

The plan is a FUJI PID with the self learn and controlled by Artisan, or that's at least where my current focus is until I run into something to make me change direction...